linux-kernel - Re: [PATCH 07/12] i2c: qup: use the complete transfer length to choose DMA mode

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Date:   Tue, 27 Feb 2018 15:01:04 -0700
From:   "Christ, Austin" <austinwc@...eaurora.org>
To:     Abhishek Sahu <absahu@...eaurora.org>,
        Andy Gross <andy.gross@...aro.org>,
        Wolfram Sang <wsa@...-dreams.de>
Cc:     David Brown <david.brown@...aro.org>,
        Sricharan R <sricharan@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/12] i2c: qup: use the complete transfer length to
 choose DMA mode

Tested on Centriq 2400

Reviewed-by: Austin Christ <austinwc@...eaurora.org>

On 2/3/2018 12:58 AM, Abhishek Sahu wrote:
> Currently each message length in complete transfer is being
> checked for determining DMA mode and if any of the message length
> is less than FIFO length then non DMA mode is being used which
> will increase overhead. DMA can be used for any length and it
> should be determined with complete transfer length. Now, this
> patch introduces DMA threshold length and the transfer will be
> done in DMA mode if the total length is greater than this
> threshold length.
> 
> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
> ---
>   drivers/i2c/busses/i2c-qup.c | 15 +++++++++------
>   1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
> index 6227a5c..a91fc70 100644
> --- a/drivers/i2c/busses/i2c-qup.c
> +++ b/drivers/i2c/busses/i2c-qup.c
> @@ -192,6 +192,8 @@ struct qup_i2c_dev {
>   	bool			is_dma;
>   	/* To check if the current transfer is using DMA */
>   	bool			use_dma;
> +	/* The threshold length above which DMA will be used */
> +	unsigned int		dma_threshold;
>   	struct			dma_pool *dpool;
>   	struct			qup_i2c_tag start_tag;
>   	struct			qup_i2c_bam brx;
> @@ -1294,7 +1296,8 @@ static int qup_i2c_xfer_v2(struct i2c_adapter *adap,
>   			   int num)
>   {
>   	struct qup_i2c_dev *qup = i2c_get_adapdata(adap);
> -	int ret, len, idx = 0;
> +	int ret, idx = 0;
> +	unsigned int total_len = 0;
>   
>   	qup->bus_err = 0;
>   	qup->qup_err = 0;
> @@ -1320,14 +1323,13 @@ static int qup_i2c_xfer_v2(struct i2c_adapter *adap,
>   				goto out;
>   			}
>   
> -			len = (msgs[idx].len > qup->out_fifo_sz) ||
> -			      (msgs[idx].len > qup->in_fifo_sz);
> -
> -			if (is_vmalloc_addr(msgs[idx].buf) || !len)
> +			if (is_vmalloc_addr(msgs[idx].buf))
>   				break;
> +
> +			total_len += msgs[idx].len;
>   		}
>   
> -		if (idx == num)
> +		if (idx == num && total_len > qup->dma_threshold)
>   			qup->use_dma = true;
>   	}
>   
> @@ -1587,6 +1589,7 @@ static int qup_i2c_probe(struct platform_device *pdev)
>   
>   	size = QUP_INPUT_FIFO_SIZE(io_mode);
>   	qup->in_fifo_sz = qup->in_blk_sz * (2 << size);
> +	qup->dma_threshold = min(qup->out_fifo_sz, qup->in_fifo_sz);
>   
>   	fs_div = ((src_clk_freq / clk_freq) / 2) - 3;
>   	hs_div = 3;
> 

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